Minimum-phase filters are limited to 6dB/oct steps, but you can use shelwing filters to achieve what you are looking for here: just set the Q to some very low value and play with the cutoff frequency.

When using linear-phase filters you can enter any multiple to 1dB/oct value, and choose the cutoff frequency you want. It will naturally be -6dB at that frequency, and 0dB at DC (which is always faaaaar away with a log scale ). So for example if you want -6dB at 20kHz then choose that as the cutoff frequency, and then play with the slope to get it "start" where you want it to.

Having a straight line magnitude response starting at some defined frequency like you show in your screenshot could be implemented with linear-phase. I would rather have a more natural and softer knee, personally, but it is doable. It would be a "difficult" target to achieve with a limited number of taps though and the knee would always end up softer.
I could look into that in some future version.

(slope is not "constant" whatever the corner frequency.).Depending of the choice of the "tilt"
In fact,-3dB (or -6dB) at 20 KHz in every case.
Purpose is to "finish" at -3dB(or -6dB) with any sloping region.

Let’s say you have a high efficiency midbass in a half fiberglass half metal enclosure (car kick panel perhaps) no clue on the volume but a guess would be about .1cuft

And let’s say that enclosure rings really badly , like between 100-300hz somewhere
The ringing is so horrific it’s simply not usable.

So you cut a hole in the back of the enclosure and vent it to the outside of this hypothetical car. You drill a 3.5” hole and vent it to the outside. Some of the ringing is gone but some remains , you proceed to now make it a very leaky to inside of the car by drilling more holes in it. The ringing subsides for the most part and becomes usable to some degree, but still has a nasty bump that sounds hollow let’s say at 150hz

You’ve done what you can to make it work but you are not able to change the enclosure any more, it has to be installed and has to sound better.

You do some close mic measurements. With the speaker out (let’s say it’s. 2118h we all know that driver) it plays flat and rolls off at 200, your measurements show a nice smooth phase response and as it rolls off the phase goes the other way (naturally of course)

You put the speaker in the enclosure and remeasure, it looks mostly the same except the phase is much steeper. And at 80 has several wraps

Do you eq the response flat so the wraps go away because of the added gain and so it stays on the graph or is that going to mess up your next measurement to find out what phase to move to help that box ringing calm down........

I ask because if the ringing is a artifact of the enclosure and the ringing is so severe the measurements are hard to read.

Letís say you have a high efficiency midbass in a half fiberglass half metal enclosure (car kick panel perhaps) no clue on the volume but a guess would be about .1cuft

And letís say that enclosure rings really badly , like between 100-300hz somewhere
The ringing is so horrific itís simply not usable.

So you cut a hole in the back of the enclosure and vent it to the outside of this hypothetical car. You drill a 3.5Ē hole and vent it to the outside. Some of the ringing is gone but some remains , you proceed to now make it a very leaky to inside of the car by drilling more holes in it. The ringing subsides for the most part and becomes usable to some degree, but still has a nasty bump that sounds hollow letís say at 150hz

Youíve done what you can to make it work but you are not able to change the enclosure any more, it has to be installed and has to sound better.

You do some close mic measurements. With the speaker out (letís say itís. 2118h we all know that driver) it plays flat and rolls off at 200, your measurements show a nice smooth phase response and as it rolls off the phase goes the other way (naturally of course)

You put the speaker in the enclosure and remeasure, it looks mostly the same except the phase is much steeper. And at 80 has several wraps

Do you eq the response flat so the wraps go away because of the added gain and so it stays on the graph or is that going to mess up your next measurement to find out what phase to move to help that box ringing calm down........

I ask because if the ringing is a artifact of the enclosure and the ringing is so severe the measurements are hard to read.

How to determine that correctly?

Thanks

Well I figured it out by trail and error

I used a combination of linear phase eq and minimum phase eq
Mostly linear phase eq

Which is wierd , I tryed linear phase eq before and it sounded echoed
However , the kick panel pod sounds echoed, so it makes sense to me now why

Phase and mag measurement is much better.
I can do a close measurement and see the crossover and the phase no more wrapping and doing wierd stuff

Oh and I also had my axis off was zoomed in way too much
But now even zoomed itís looking good

Listening to it the harmonics sound so much better and natural.
Wow I love rephase even more now. What an amazing tool!

(slope is not "constant" whatever the corner frequency.).Depending of the choice of the "tilt"
In fact,-3dB (or -6dB) at 20 KHz in every case.
Purpose is to "finish" at -3dB(or -6dB) with any sloping region.

I like the idea and will definitely look into implementing such a feature in a future version

Is this ringing due to internal reflections, or panel resonances?
Does filling it with fiberglass help the matter?
If these are resonances of thin metal panels you might try adding automotive damping sheets on them.

The issue is the cavity walls. There so close to the basket and the air volume is tiny. Even vented to the outside it adds a echoed ringing

Iíve done all the dampeners (wouldnít have posted this if I havenít exhaust all efforts.)

Trying to understand what makes this happen.

Go mount a midrange in a coffee can and put dampeners on the coffee can , it will still sound like itís in a can. Dampeners lower the resonance frequency by adding mass. At some point itís still in a tiny little chamber, the only option left is remove the mount and run it as a baffle-less dipole (which actually sounds better than this Iíve tried it).

I got the measurements to look better, at least I can do something with them.
I was wondering what is the norm for how a measurement should look when a speaker is in way too small enclosure. What happens to the speaker and what can typically be done in dsp/fir to mitigate some of its effects.

Iím kinda hoping for some ideas I havenít thought of. Iíve read everything I can about it. I think Iím past that part and am venturing into uncharted territory with fir in car. So the most info I can possibly get to get me thinking the right direction is invaluable to me and so much appreciated!

So no doubt you are getting reflections from the can coming back through the cone. Call it can honk, a relative of horn honk, which has been diagnosed as mouth reflections. Gunness filtering (google is your friend) would be an elegant solution but its shall we say challenging for a DIYer. If Pos would help, it might approach feasibility. The basic idea is to cancel the reflections by injecting a delayed copy of the signal into the input of equal magnitude and opposite polarity. Easy to say, hard to do.

As you shrink the size of the metal can you approach a sealed back midrange. Perhaps you should try to seal the back of your midrange. This will minimize the delay of the reflections that come back through the cone so that the frequencies at which they interfere are out of band.